It requires but little imagination to conceive that a very slight subsidence of the country in North Wales lying between the Vale of Clwydd and the estuary of the River Dee would convert it into a peninsula consistingof Carboniferous rocks skirting to the north, and to the east a strip of Silurian ground. The backbone of this peninsula is composed of Lower Carboniferous rocks, forming the high range which starts from the bold cliffs that border the sandy flats of the north shore of Flint from Dyserth to Talacre. Stretching southwards by way of Halkyn Mountain, Moel Findeg, Nerquis Mountain to Minera and Llangollen, this range, in the main, forms ani anticline, off whose eastern flanks the higher divisions of the Carboniferous system dip in natural sequence towards the River Dee.